In a typical electrophotographic machine (e.g. copier, duplicator, printer, etc.), a continuous loop of a photoconductor film is commonly used to transfer an image from an input section onto a copy medium (e.g. a sheet of paper or the like). The film is initially charged and passed through an input section where an image is projected onto the charged film. The film then moves through a developing section where toner is applied to the charged image, and on through an image transfer section where the toner is transferred to a sheet of paper or some other medium. The toner (i.e. image) is then fixed (i.e. fused) to the sheet by passing the sheet between a pressure roller and a heated roller within the fuser section of the machine.
In electrophotographic machines of this type, it is common to use a vacuum transport to transfer the sheet from the film loop to the fuser section. Often this vacuum transport is directly interfaced between the film and the fuser section wherein the vacuum transport receives the sheet from the film and passes it directly into nip between the rollers in the fuser section. This requires that the surface speeds of (a) the film loop, (b) the vacuum transport belt(s), and (c) the fuser rollers all have to be closely matched. If the speeds become mismatched, there may be relative movement between the film and the sheet while the image is being transferred onto the sheet thereby resulting in smearing of the image on the sheet.
To alleviate this problem, some commercial machines have now abandoned any direct interface between the film and the fuser section and instead, use a curved or arched travel path between the image transfer and the fuser sections which is longer than the straight-line distance between these sections (i.e. longer than the length of any sheet to be used in the copy operations). This extended path effectively “de-couples” the speed of the fuser rollers from the speed of the film thereby eliminating the possibility of relative movement between the sheet and the film as the toner image is being transferred. 
Such an extended, curved travel path is typically provided by angling the vacuum transport away from the straight-ine distance between the sections and then positioning a fuser entrance guide between the exit end of the vacuum transport and the entrance of the fuser section. The fuser guide is normally vacuum assisted so that the sheet is held against the guide and hence, properly oriented as the sheet enters the fuser section. This type of curved travel path and guide is known and have been commercially used, e.g. DIGIMASTER 9110, Heidelberg Digital L.L.C., Rochester, N.Y.
As a sheet moves along this type of extended travel path, it is particularly important to prevent the sheet from falling away from the fuser entrance guide as the trail edge of the sheet moves across the guide and into the fuser section. If the sheet should drop, it may contact and slide across other elements in the paper path before it enters the fuser section. If this happens, it is likely that smearing of the unfused image on the sheet will occur.
Ideally, the vacuum being applied at the guide will be strong enough to hold the sheet in contact with the guide's surface until the sheet has completely entered the fuser. While providing such a strong vacuum would normally present no problem, it must be recognized that this vacuum can not be too strong or it will cause the sheet to slow down significantly or to stall completely on the guide's surface thereby resulting in serious jamming problems or the like. Therefore, it is important to maintain the vacuum force at the guide so that it will hold a sheet in contact with guide surface as the sheet moves across the guide but, at the same time, will allow the vacuum transport to readily move the sheet across the guide and into the fuser.
Unfortunately, however, in machines of this type, there are other factors, which affect the sheet as it moves along the paper travel path within the machine. For example, as the sheet passes across the gap between the exit of the vacuum transport and the entrance of the fuser guide, the sheet is routinely subjected to unwanted air currents within the machine. These air currents are those which are inherently generated by the common air movers (e.g. cooling fans, etc.) within the machine which are necessary for regulating the internal machine temperature, removing contamination, etc.
During operation, these air currents blow onto the sheet as it passes through the gap between the vacuum transport and the fuser guide and act in opposition to the vacuum being applied at the guide. That is, the air currents blow against the sheet and try to force it away from the surface of the guide while the vacuum tries to hold the sheet against this surface. If one merely provides a stronger vacuum to compensate for these air currents, the resulting vacuum is likely to be so strong that it will cause the sheet to slow or stall as the sheet moves across the guide, which is unacceptable. Further, a larger air mover would be required to produce the necessary vacuum. 
Accordingly, it is highly desirable to protect the sheet from these air currents as the sheets moves along the paper travel path and into the fuser section of the machine so that the vacuum can be maintained within a range strong enough to hold the sheet against the guide but not so strong as to slow or stall the sheet at the guide.